When I draw a line in preview it shrinks

I have a MBP late 2015, running High Sierra 10.13.2

When I use preview I often will write little marks on an article I'm reading to put a nondistracting line or because I have access to more colors. But, since upgrading to High Sierra, possibly before, I have had an issue where everything I draw will shrink significantly. I will draw a line about this big ________ and 3x as think, but when I let go of the trackpad it shrinks into this ___ at about the same thickness. It kills me.

I am unable to underline or put brackets around large paragraphs without them shrinking into the document. I have changed the thickness, tried making longer lines to compensate and it always shrinks to an unusable size.

I cant find this anywhere on google or in the search section of this support community.

Any help would be huge. When finals are over I will be going to the Apple store because I also have issues with my trackpad– the pinch to zoom stops. You don't think that is connected, do you?

Any help would be great, thanks!